1. Field of the Invention
The present invention relates to a radiation inspection apparatus that inspects an inspection target using radiation.
Priority is claimed on Japanese Patent Application No. 2011-042240, filed Feb. 28, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
A radiation inspection apparatus is an apparatus which inspects an inspection target by irradiating radiation (for example, electromagnetic waves with a wavelength of 10 micron or more, such as X-rays, β-rays, γ-rays, ultraviolet rays, visible rays, infrared rays, and radio waves) to the inspection target and detects the radiation transmitted through the inspection target so as to obtain permeation characteristics. The radiation inspection apparatus has been used in various fields due to the features by which characteristics of the inspection target may be inspected without damaging the inspection target. For example, in the field of production, the radiation inspection apparatus is often used as a thickness inspecting apparatus to inspect the thickness or the amount of coating of a produced sheet or film (a single-layer film and a multi-layer film) online.
Here, thickness inspecting apparatuses is broadly classified into “scanning type inspection apparatuses” and “whole surface inspection type inspection apparatuses.” The former “scanning type inspection apparatus” is an apparatus that has, for example, a configuration in which a radiation source head generating radiation and a detector head such as an ionization chamber are disposed so as to face each other with an inspection target interposed therebetween and both heads are movable together in a reciprocating manner in a direction (the width direction of the inspection target) intersecting a direction in which the inspection target flows. In contrast, the latter “whole surface inspection type inspection apparatus” is an apparatus that has, for example, a configuration in which a radiation source head generating radiation extending in a line shape in the width direction of an inspection target and a detector head with a line type detector having a plurality of detection elements arranged in the width direction of the inspection target are disposed so as to be fixed with the inspection target interposed therebetween.
The “scanning type inspection apparatus” measures the distribution of the thickness of the inspection target in the width direction by detecting the radiation irradiated from the radiation source head using the detector head while moving the radiation source head and the detector head together in a reciprocating manner in the width direction of the inspection target. In contrast, the “whole surface inspection type inspection apparatus” measures the distribution of the thickness of the inspection target in the width direction by detecting the linear radiation irradiated from the radiation source head using the line type detector of the detector head without moving the radiation source head and the detector head. Furthermore, Japanese Examined Utility Model Application, Second Publication No. H7-52573 and Japanese Unexamined Utility Model Application, First Publication No. S62-193505 respectively disclose the “scanning type inspection apparatus” and the “whole surface inspection type inspection apparatus” of the related art.
Incidentally, in the thickness inspecting apparatus, the inspection precision may be degraded due to reasons such as degradation in the radiation source head with the passage of time, a variation in the sensitivity of the detector, and a variation in the environment (periodic variations in the temperature and the humidity according to the weather, the time of day, or the like). For this reason, in any thickness inspecting apparatus between the “scanning type inspection apparatus” and the “whole surface inspection type inspection apparatus,” there is a need to perform a correction in a state in which the inspection target is first removed and the radiation from the radiation source head is directly irradiated to the detector head.
The entire length of a production line used to conduct continuous production is as long as several tens to a hundred and several tens of meters, and the inspection target (product) may not be easily removed during the production. For this reason, for example, the best timing for the correction is considered to be a timing at which the inspection target is stopped so as to change the type of product or to pause the production. However, recently, production has often been conducted so that the inspection target is not stopped even for a short period of time by allowing a current product and a next product to be selected to be continuous to each other using a dummy sheet even when the type of product is changed, in order to improve the yield rate. Under the environment in which such production is conducted, the inspection target or the dummy sheet is normally present between the radiation source head and the detector head, which makes it difficult to perform a precise correction.
Here, in any thickness inspecting apparatus between the “scanning type inspection apparatus” and the “whole surface inspection type inspection apparatus,” if an evacuation position is provided so as to allow the radiation source head and the detector head to face each other without interposing the inspection target or the dummy sheet therebetween, the precise correction may be performed even in a state in which the inspection target is not stopped. In the “scanning type inspection apparatus,” the radiation source head and the detector head are small in size and do not need a large evacuation position. Accordingly, countermeasures of performing the correction by forming the evacuation position are realistic. However, since the “whole surface inspection type inspection apparatus” includes the detector head with a length approximately equal to the width of the inspection target, there is a need to form an evacuation position with a length approximately equal to the width of the inspection target. However, in a real production site, various units are often arranged with the narrowest gap therebetween so as to reduce the footprint. For this reason, it is not realistic to ensure the evacuation position with a length approximately equal to the width of the inspection target.